The present invention relates to caster assemblies, and more particularly to a heavy-duty caster having a swivel plate mounted on the upper surface of a wheel-carrying horn member. Casters of this type are used extensively in heavier load applications such as supporting work dollies, pallets and scaffolding equipment. In such heavier-load applications, an axial thrust bearing, such as a ball-bearing assembly, is provided between the swivel plate and the upper surface of the horn to reduce the frictional resistance to swiveling motion and to distribute the load evenly to the horn from the supported equipment.
In one known swivel plate type caster, the caster assembly includes an inverted generally U-shaped horn member that supports the wheel for rotation, that has an upper portion with a recess that receives large metal ball-bearings also received in a mating recess in the lower surface of a round or square swivel plate adapted to be fastened to the under portion of the article or equipment to be supported. The swivel plate is axially fixed to the upper portion of the horn member by a central pin fixed thereto that extends through the horn member and carries in some cases a secondary ball-bearing thrust member on the underside of the horn member, also including an annular array of smaller metal ball-bearings engaging the underside of the upper portion of the horn.
In many environments where heavy-duty swivel plate casters are utilized, moisture, humidity, chemically corrosive materials and liquids cause the metal parts of the caster to rust and corrode, and while some rust and corrosion on certain parts of the caster does not detract from the function of the caster, only its appearance, it is frequently found that rust and corrosion in the primary and secondary thrust bearing areas of the caster eventually leads to bearing failure from a breakdown in the integrity of the steel ball-bearings. In the food-processing industry for example, high humidity, salt and brine are frequently found in the plant environment and severely attack presently known swivel plate type casters.
Other examples of industries having corrosive chemical handling problems and chemical manufacturing and processing, agricultural chemical, pulp/paper, petro-chemical, metal plating, paint and textiles.
Anti-corrosive plastic bearings have been devised in the past, but thus far have not found success in heavy load casters for two reasons. Firstly, such plastic bearings do not have high load resistance or capacity, and they frequently fail even if ball-type bearings. Moreover, ball-type plastic bearings deform under high loading and substantially retard rotational motion and hence if used on this type of caster would inhibit pivoting movement of the swivel plate on the horn.
While polytetrafluoroethylene (TEFLON) coatings have been known to inhibit corrosion of metal parts, there has never been devised insofar as I am aware, a high load non-corrosive caster bearing used with such a coating. Metal ball-bearings used with fluorocarbon coated parts would continue to fail in highly corrosive environments, and moreover would have a high frictional coefficient when used with such coatings.
It is the primary object of the present invention to provide a non-corrosive swivel type caster that ameliorates the problems noted above in the prior art.